Microorganism is a general term of tiny organisms which are widely distributed in nature, are not visible to the naked eyes but can be observed only after being magnified at hundreds of times, thousands of times or even tens of thousands of times under an optical microscope or an electron microscope. Their characteristics include a tiny size, a simple structure, rapid reproduction, easy variation and strong adaptive capacity to environment.
Microorganisms are of wide varieties, and are extremely widely distributed in nature. A variety of microorganisms are also present on body surfaces and cavities communicated with exterior of human, animals and plants.
One of the most important influences of microorganisms on human is to cause some diseases, especially infectious diseases. Although the human has made great progress in the prevention and treatment of diseases, newly occurring and recurring microbial infections continue to occur, and many diseases are lack of effective therapeutic drugs all the time. Furthermore, the wide abuse of broad-spectrum antibiotics causes a strong selection pressure, so that many strains mutate, resulting in more dangerous drug-resistant strains.
All microorganisms growing on or in a living body are called parasitic microorganisms, and the microorganisms in parasitic make a living through depriving nutrition of other organisms, even depending on some parts of the bodies of other organisms as nutrients. Microorganisms can enter a human or animal body through the mouth, skin or respiratory tract, and grow and reproduce by using the nutrition of the human or animal body. If these bacteria produce toxins, the host will fall ill, such as of cholera, typhoid and pneumonia. Diseases such as AIDS and common cold are caused by viruses. Viruses are comparatively more specific parasitic microorganisms; because they cannot live outside of living cells, they are called strictly parasitic microorganisms.
Microbial infections are common clinical diseases caused by microorganisms. For the diagnosis of most of bacterial diseases, bacteriological diagnosis is required in order to determine the causes of diseases. However, isolating bacteria from a specimen does not necessarily mean that this bacterial species is the pathogen of the disease, and thus a comprehensive analysis shall be performed according to the clinical situation of the patient, the specimen collection site, and the species of the acquired bacteria. Sometimes virulence, cell and animal tests shall be made to determine pathogenicity of the strain.
Since bacteria and their metabolites have antigenicity, bacterial infections can also be diagnosed by detecting antibodies. Furthermore, gene diagnosis, a new method for diagnosing bacteria by detecting genetic materials of bacteria, is developed in recent years. However, the detection method mentioned above requires tedious operation and strict sample collection and preservation conditions, but also has a high false positive rate in the test results and a long detection period, which could easily lead to delay of the patient's treatment.
An infectious disease, especially a chronic persistent infection, is one of global stubborn diseases harmful to the human health and life. Intracellular pathogens that pose significant impact on human include Mycobacterium tuberculosis, Salmonella, Brucella, Legionella pneumophila, Listeria, and Mycobacterium leprea. Seven diseases, including tuberculosis, AIDS and hepatitis, form global threats, and the reason why they are difficult to treat is closely related to the intracellular parasitism of pathogens.
It is a difficult problem to treat intracellular microbial infections. The main reason includes: when the pathogens invade and lie dormant in the cells, it is difficult to deliver a conventional antibiotic to the cells where the pathogens hide, and even if delivered, it is difficult to achieve an effective microbicidal effect at the concentration of antibiotic; antibodies could hardly enter the cells to play a role; and after the intracellular bacteria are successfully living in cells, they could not only escape from the immune phagocytosis, killing and clearance, but also exist for a long time in the cells and lead to disease of the body at the appropriate time (e.g., when immunity of the body decreases).
Salmonella is a large group of Gram-negative bacilli which live in the human and animal intestinal tracts and have similar biochemical reactions and antigen structures, of which some are specifically pathogenic to humans, some are only pathogenic to animals, and some are pathogenic to both humans and animals, which are collectively referred to as Salmonella. Not less than 1800 kinds of Salmonella have now been found, and are divided into A, B, C, D, E and other basic bacterial types depending on the antigen constituents. The strains relevant to human diseases mainly include paratyphoid A bacilli in group A, paratyphoid B bacilli and Salmonella typhimurium in group B, paratyphoid C bacilli and Salmonella cholerae in group C, and Salmonella typhi and Salmonella enteritidis in group D. The bacteria may cause fowl typhoid, pullorum disease, cholera hog, Salmonella typhimurium disease, swine paratyphoid, Equi salmonellosis disease and other diseases. Salmonella cholerae has the strongest pathogenicity, and then are Salmonella typhimurium and Salmonella enteritidis. Salmonella infections or eating foods contaminated with faeces of carriers may induce food poisoning.
Therefore, in order to control microbial infectious diseases, there is an urgent need to develop new diagnostic and therapeutic techniques with simple operation and accurate results so as to improve the laboratory diagnosis and clinical treatment of such diseases to avoid delays of the patient's condition and reduce the physical and economic burden of patients.